Saves an errno per-thread, retrieved via _get_errno(), instead of
changing the value of a global variable during context switches to avoid
a hit to the context switch performance.
Per-arch asm implementations are provided for maximum performance.
Enabled by default, but can be disabled via the CONFIG_ERRNO option.
Change-Id: I81d57a2e318c94c68eee913ae0d4ca3a3609c7a4
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>